Perhaps you should read Roberts' book to see the evidence he has found to substantiate his point?
There were at least two assassination attempts against Napoleon when he was First Consul. Both were attempted by the Bourbons/Royalists who were in England and supported by the British government, and at least one of the attempts was actively supported by the British government.
This isn't new information and Vincent Cronin talks about these assassination attempts in his biography of Napoleon which was first published in 1972.
So, it looks like Andrew Roberts has a point...